1. Field of the Invention
The present invention relates to a gasket and mandrel assembly, including a flexible gasket and a pair of mandrels, for use in casting the gasket in place within the wall of a concrete structure, wherein the gasket provides a sealed joint between the concrete structure and a pipe.
2. Description of the Related Art
In general, pipe joint gaskets or seals are well known in the art for sealing a pipe joint connection between a pipe and a structure to which the pipe is connected. In one particular application, for example, a pipe joint is formed between a sewer pipe and a concrete manhole riser, in which a sewer pipe is inserted through a gasket which is embedded within the concrete wall of the manhole riser. In other applications, pipe joints may be provided to connect pipes to septic tanks, for example, or may be provided in any other structures to which pipes are connected.
One known type of pipe joint connection between a concrete structure and a pipe is shown in FIGS. 1 and 2. Referring to FIG. 1, an annular cast-in gasket 10 is shown, which is cast within the wall of a concrete structure 12. Concrete structure 12 typically includes a curved wall 14 having an opening 16 which is formed within wall 14 when gasket 10 is cast in place within wall 14. Gasket 10 generally includes an anchoring portion 18 extending radially outwardly thereof for embedment within the concrete of structure 12, and a compressible sealing portion 20 extending radially inwardly thereof to sealingly engage the outer surface of a pipe 22 inserted through gasket 10, as shown in FIG. 2, to provide a fluid tight seal between pipe 22 and wall 14 of concrete structure 12.
Gasket 10 is cast within concrete structure 12 using a pair of mandrels, including conically-shaped front and rear mandrels 24 and 26, respectively. Front and rear mandrels 24 and 26 are each generally annular in shape, and include outer walls 28 and 30, respectively, which are disposed at an angle which is inclined at least 10° with respect to the common longitudinal axis L1—L1 of gasket 10 and the resulting opening 16 which is formed in concrete structure 12. In particular, it is desirable that outer walls 28 and 30 of mandrels 24 and 26 are inclined at an angle of at least 10° with respect to the longitudinal axis L1—L1 in order to facilitate the easy removal of mandrels 24 and 26 in opposite directions along longitudinal axis L1—L1 from opening 16 in the concrete structure 12 after the cast concrete has cured.
After mandrels 24 and 26 are removed, gasket 10 is anchored in place by the embedment of anchor portion 18 of gasket 10 within the cured concrete of structure 12. It is also desirable for the inner surfaces of opening 16, which are formed by outer walls 28 and 30 of mandrels 24 and 26, to be angled at least 10° with respect to the longitudinal axis L1—L1 in order to accommodate tilting movement of pipe 22 in which pipe 22 becomes misaligned with longitudinal axis L1—L1. Other similar gaskets which are cast in place in a similar manner to the foregoing gasket 10, using similar mandrels, may include a pipe sealing portion which extends along the longitudinal axis L1—L1 of the gasket, with the pipe sealing portion externally clamped to the outer surface of a pipe using a clamping band to provide a fluid tight seal between the gasket and the pipe.
Although the foregoing types of gaskets and mandrels have been effective for forming concrete structures with cast-in gaskets for providing sealed joints between the concrete structures and pipes, a problem with the gaskets and mandrels is that it is possible to cast the gaskets incorrectly within the concrete structures when the structures are initially formed, such as, for example, positioning the gasket incorrectly during casting of the structure. Failure of the gasket in the field after a pipe is connected to the gasket is also possible. In each of these circumstances, repairing or replacing the gasket is often difficult, if not impossible, without re-casting a portion of the concrete structure or replacing the entire concrete structure.
What is needed is a gasket and mandrel assembly for pipe joints which is an improvement over the foregoing.